Electrical stimulation of the central nervous system (CNS) has been used as a treatment for a number of disorders. Microelectrode arrays are used to achieve high spatial selectivity with micro-machined penetrating shanks. Caused by tethering forces from interconnects, the rigid bodies of these shanks result in chronic responses that include scarring and reduces the effectiveness of such micro stimulators.
Wireless stimulators are expected to mitigate this chronic response because they have no wires to cause forces from micromotion and therefore are free to float. Some examples of wireless stimulators include addressable radio-frequency (RF) microstimulators and an RF microstimulator array. These devices receive energy and communication information from RF electromagnetic waves. This necessitates an inductive coil that limits the minimum size of the device.
Photovoltaic stimulators have the ability to float, similar to RF stimulators, but they convert optical energy into electrical energy using semiconductors. Fiber guided high-efficiency photovoltaic stimulators have been used for neurostimulation. Retinal photovoltaic arrays exploit the two-dimensional nature of sight and utilize an image projection system to selectively activate photodiodes in an array. Additionally, gene therapy technologies have enabled photonic neurostimulation in neurons that have algal proteins.
Floating Light Activated Microelectrical Stimulators (FLAMES) with have been micromachined and tested in tissue. FLAMES devices exploit the dispersive nature of white and grey matter to cause neurostimulation without a focused optical path. As seen in FIG. 1a, FLAMES devices are indiscriminately activated whenever enough optical energy is converted into electrical energy. However, there is a need to have selectively addressable stimulators to allow more directed stimulation which would open up a wide range of potential applications that are currently not possible.